Introduction

This page provides up-to-date information about using the SPIRE instrument: from preparing observations to reducing your data. This page also provides you with the latest calibration accuracies and known SPIRE calibration issues.

Reducing SPIRE data

Software and documentation

HIPE (Herschel Interactive Processing Environment): The latest User Release version that you should use for reducing SPIRE data can be downloaded from this link.

Within HIPE you can access all the SPIRE data reduction and HIPE-user documentation. The SPIRE Data Reduction Guide (SDRG) follows the user pipeline scripts and also explains the details of pipeline processing and data analysis. It is also available online here:

The SPIRE Launch Pads

The SPIRE Launch Pads are single sheet quick entries (like a cheat sheet) into SPIRE data reduction and providing quick references to the relevant sections in the SPIRE Data Reduction Guide. There are launch pads for Data Access, SPIRE Photometer and Spectrometer data reduction.

Spectrometer data reduction

Spectrometer Overview

The best source of information for reducing SPIRE Spectrometer data is the SPIRE Data Reduction Guide available through the HIPE help. This runs through the User Pipeline scripts step by step, describes several other Useful Scripts, and offers advice for specific types of sources:

Faint (< 10 Jy) and medium (< 100 Jy) strength sources

Bright sources (> 500 Jy)

Semi-extended sources

Spectral mapping observations

Observations with few repetitions

For faint sources, the subtraction of instrument, telescope and background emission is particularly important. Optimum subtraction can be performed in several ways (read the SPIRE Data Reduction Guide for details):

Subtract the spectrum of surrounding detectors (use the "Background Subtraction" script in HIPE)

Subtract a Dark Sky spectrum observed close in time to your observation (use the "Background Subtraction" script in HIPE)

The Dark Sky observation should have at least the same number of repetitions as the observation it is going to be subtracted from.
Dark Sky observations are observed on every SPIRE Spectrometer OD, and are all public in the Archive.

Spectrometer Data Processing Issues

Photometer data reduction

Photometer Overview

The best source of information for reducing SPIRE Photometer data is the SPIRE Data Reduction Guide available as a standalone hyperlink document as well as through the HIPE help. This runs through the User Pipeline scripts step by step, describes several other Useful Scripts, and offers advice for specific issues that might be encountered.

Photometer Data Processing Issues

Known Issues in ODs 1304 & 1305

For (yet) unknown reasons, the three detectors PSW-B5, PSW-E9 and PSW-F8 - that use to behave well during the entire mission - were noisy during the two operational days 1304 and 1305. The result are stripes visible in the final PSW map which the current (HIPE 11) pipeline is not able to correct. The solution is to mask and exclude these detectors from the analysis. This could be done in 2 ways:

You can use the SpireMaskEditor GUI as described in Sec. 8.4 of the SPIRE Data Reduction Guide: write-click on your observation context variable and then select Level1_SpireMaskEditor and set to Master all samples in all scans (listed as BBID) for the detectors mentioned above.

After either of those cases, you must then re-run level 1 to 2 steps on the newly modified level1 product. If your observation has been already re-reduced with HIPE 11, original and new level1s are already destriped, so you can directly run the naive map-maker on the new level1. Otherwise, you must run the destriper step: check the pipeline script for details.

As of HCSS 11, a new task named zeroPointCorrection is available to the users: this task calculates the absolute offset for a SPIRE map based on cross-calibration with HFI-545 and HFI-857 maps, colour-correcting HFI to SPIRE wavebands assuming a grey body function with fixed beta.

Source Extraction and Photometry

The current recommended method for photometry sourceExtractorTimeline task (formerly known as the Timeline Fitter) which works on the detector timelines. The Map based algorithm sourceExtractorSussex (SUSSEXtractor) providers good results and is useful on larger maps where the sourceExtractorTimeline will be significantly slower. sourceExtractorDaophot (DAOphot) also provides a reasonable estimate of the source flux but may require an aperture correction.

Photometry on single direction fast scan parallel mode maps:

The photometry on single scan direction fast parallel mode results in higher photometric errors of up to 5 percent for aperture photometry compared to nominal speed and cross linked maps. The best results are obtained using the Timeline Fitter. Wherever possible orthogonal and nominal direction parallel scans should be merged.

Currently no astrometry correction is made during the merging process for parallel maps. For fast parallel mode an astrometry offset may be present which can in cases where there is a large offset, result in reduced photometers accuracy of the order of up to 25% compared to large cross-linked scan maps.

In HIPE13 (and HIPE 11), the default PRF used by SUSSEXtractor has a size of 5x5 pixels. In HIPE 12, a PRF of size 13x13 was used to allow a more complete coverage of the PRF edges, but this lead to some secondary effects that negatively affected the measured flux densities. If you use HIPE v12 we advise you to change the input PRF size using this script, in order to obtain the same photometry as in HIPE v13.

SPIRE report from the January 2013 HSC Map Making Workshop

The official release of the report of SPIRE map-making test campaign (2013) is available in arXiv:1401.2109, the report can also be downloaded as a PDF file.

Cookbooks

The standalone "Photometry Cookbook", is no longer maintained - it is being incorporated into the SPIRE DRG - please see the SDRG for photometry cookbook information, and raise a Helpdesk ticket if you find something missing.

SPIRE calibration file versions

The available calibration trees for SPIRE are listed below (with the current operational version at the top). The link to each calibration tree provides the changelog for this version.

Any of the calibration trees can be retrieved in HIPE from the HSA using (e.g.) cal = spireCal(calTree="spire_cal_14_3") etc. The default (applicable to the HIPE version in use) can be obtained with cal = spireCal(calTree="spire_cal"). It can then be saved to a local pool right-clicking on the cal variable and then selecting from the context menu Send To -> Local Pool.

Alternatively, the latest calibration tree for SPIRE can be obtained as a jar file from Latest calibration trees. Then, you have two possibilities to read and save:

The jar file can be load directly into HIPE with the command: cal = spireCal(jarFile="PATH_TO_FILE/spire_cal_14_3.jar"). To save it to a local pool, proceed as described above, right-clicking on the cal variable and then selecting from the context menu Send To -> Local Pool.

The jar file can also be saved directly to a local pool without opening HIPE, running the following command in the terminal command line: cal_import PATH_TO_FILE/spire_cal_14_3.jar. Then, to load the calibration tree in HIPE, simply type: cal = spireCal(pool="spire_cal_14_3")

The individual calibration files (FITS tables or FITS images) in the jar file can be listed with jar tvf spire_cal_14_3.jar and extracted with jar xvf spire_cal_14_3.jar FILENAME. Details of individual calibration products can be found here, usually the Name column matches the FITS file name.

SPIRE calibration and performance

Photometer calibration and uncertainties

SPIRE Photometer Calibration:Full details of the SPIRE calibration can be found in the SPIRE Handbook and in dedicated publications: the calibration scheme is described in Griffin et al. (2013) and the implementation using Neptune as the primary calibration standard, is described in Bendo et al. (2013).

Calibration uncertainties, which should be included in addition to the statistical errors of any measurement, are as follows:

▒ 4% absolute from Neptune model (this uncertainty is systematic and correlated across the three bands)

▒ 1.5% (random) from Neptune photometry

Extended emission calibration

In addition to the above uncertainties, there is an additional ▒1% uncertainty due to the current uncertainty in the measured beam area

SPIRE Photometer Beams:

A final analysis of the SPIRE beam profiles was completed in Oct 2014, taking into account so called "shadow" observations that were taken after Neptune had moved away. This dramatically reduced the uncertainties in the beam profile solid angles to better than 1%. It also eliminated the need for a "static" part in the semi-empirical beam profile model. The results at a scale of 1 arcsec/pixel as well as the data needed for the model are available for download. A detailed description of the analysis is available too.

These new beam maps and radial profiles are available also in the latest SPIRE calibration tree (BeamProf, RadialCorrBeam).

SPIRE Photometer filter transmission curves:

These are available in the SPIRE calibration context (photRsrf).

Neptune and Uranus models used for the SPIRE photometer flux calibration:

The ESA4 models used from HIPE v11 and spire_cal_11_0, are available here (v4 files).

The ESA2 models used up to HIPE v10 and spire_cal_10_1, are available here (v2 files).

Spectrometer calibration and uncertainties

Calibration uncertainties, which should be included in addition to the statistical errors of any measurement from HIPE v11 onwards, are as follows:

Point sources observed on the centre detectors (SSWD4 and SLWC3): The measured repeatability is 6%, with the following contributions: (i) absolute systematic uncertainty in the models from comparison of Uranus and Neptune - determined to be ▒3%; (i) the statistical repeatability determined from observations of Uranus and Neptune, with pointing corrected - estimated at ▒1% (excluding the edges of the bands); (iii) the uncertainties in the instrument and telescope model, which lead to an additive continuum offset error of 0.4 Jy for SLW and 0.3 Jy for SSW and (iv) the effect of the Herschel APE.

Sparse observations of significantly extended sources:

The conservative absolute uncertainty in intensity for a reasonably bright, fully extended object, observed in the central detectors is of the order of 4%, with the following contributions: (i) the systematic uncertainty in telescope model of 0.06%; (ii) the statistical repeatability estimated at ▒1% (iii) an additive continuum offset of 3.4x10-20 W/m2/Hz/sr for SLW and 1.1x10-19 W/m2/Hz/sr for SSW and (iv) far-field feedhorn efficiency correction of the order of 3%.

When the source extent is larger than the main beam size, but not fully extended, or if there is structure inside the beam, then the uncertainties are dominated by the source-beam coupling ( see Wu et al. 2013 ) and are greater than ▒4%.

Mapping mode: The variations between detectors is important. The overall repeatability was measured as ▒7% by Benielli et al., 2014. The off-axis detectors can be less well calibrated, especially outside the unvignetted part of the field, although this tends to only be significant for faint sources. As of HIPE 12, the vignetted detectors are included in the projected cubes as default. And as of HIPE 14, convolution projected (CP) cubes are also offered in the Observation Context level-2 products. The overall repeatability for cubes obtained from the HSA is similar to that found by Benielli et al., 2014, and has been measured as 6-10% for Naive projected cubes and 4-10% for CP cubes. The uncertainties sharply increase below 700 GHz in the SLW band, although this increased is less dramatic for CP cubes.

Uranus model used for the SPIRE FTS point-source flux calibration:

The ESA4 model, used from HIPE v10 onwards, is available here (v4 file).

Bright source mode:

The bright source mode is properly calibrated in HIPE v14.1, but not in HIPE v14.0 and v13. See the DP Known Issues page. Bright mode observations with HIPE v12 are also correct.

User contributed software and scripts

The currently available user contributed scripts and plugins are listed here.

Users are welcome to submit scripts and software that they believe could be of general interest to the community to the Herschel helpdesk.